WO1999053104A1

WO1999053104A1 - Polymer tanning agents containing n-vinyl units

Info

Publication number: WO1999053104A1
Application number: PCT/EP1999/002147
Authority: WO
Inventors: Anton Negele; Gerhard Wolf; Axel Kistenmacher; Georg Igl
Original assignee: Basf Aktiengesellschaft
Priority date: 1998-04-09
Filing date: 1999-03-29
Publication date: 1999-10-21
Also published as: KR20010042484A; ES2212847T3; DE19815946A1; US6652597B1; DE59907026D1; BR9909538A; JP2002511523A; EP1084279A1; EP1084279B1

Abstract

The invention relates to the use of polymers containing n-vinyl units, obtained by radically initiated polymerization of a monomer or a monomer mixture consisting of (A) 5 to 100 wt.% n-vinylamides or n-vinylamines; (B) 0 to 95 wt.% monoethylenically unsaturated carboxylic acids with 3 to 8 C atoms or the derivatives thereof; (C) 0 to 95 wt.% n-vinyl or C-vinyl compounds and (D) 0 or less than 10 wt.% copolymerizable monomers. Said polymers are used in the form of aqueous solutions or dispersions for self-tanning, pre-tanning or co-tanning smoothed skins and pelts and for retanning hides and fells.

Description

Polymeric tanning agents containing N-vinyl units

description

The present invention relates to the use of polymers containing N-vinyl units from N-vinylamides and / or N-vinylamines and optionally monoethylenically unsaturated carboxylic acids or their derivatives, other N-vinyl and / or C-vinyl compounds and other copolymerizable monomers in the form of aqueous solutions or dispersions as leather and fur tanning agents.

In leather production, the main tanning is usually carried out with mineral tanning agents such as basic chromium, aluminum and / or zirconium salts alone or in combination with synthetic tanning agents. Subsequent retanning with natural or synthetic tanning agents mainly serves to improve leather properties such as feel, softness, grain and fullness.

As tanning agents in retanning, for example, syntans, i.e. water-soluble condensation products from e.g. Naphthalenesulfonic acid and formaldehyde or from phenolsulfonic acid, formaldehyde and urea, also ligninsulfonic acids and also polymers and copolymers based on acrylic acid and other unsaturated polymerizable carboxylic acids, generally in combination with the aforementioned syntanes.

For example, in US-A 2 205 882 and US-A 2 205 883 the use of polyacrylic acid, of copolymers of acrylic and methacrylic acid, of styrene-maleic anhydride copolymers, of polymethacrylic acid and of copolymers of methacrylic acid with styrene or methyl methacrylate for tanning described by leather. A disadvantage of these products is that the desired fullness and grain size can often not be achieved. In addition, tendencies toward loose scars or double-skinnedness often occur with such connections, particularly in the loose structured parts of the skin. Furthermore, these products generally lighten the color, which leads to an increased consumption of dyes and thus increases the cost of the formulation.

DE-A 32 45 541, DE-A 32 48 019 and DE-A 32 48 031 are copolymers of vinylphosphonic esters, unsaturated sulfonic acid esters, the amount of these two monomers together being at least 10% by weight, acrylamide and optionally up to 30% by weight of further monomers such as N-vinylamides and / or 2 saturated monocarboxylic acids known. The copolymers are also recommended as retanning agents.

Copolymers of N-vinylcarboxamides and their mono-ethylenically unsaturated compounds such as acrylic acid, acrylic acid esters, vinyl acetate, N-vinylpyrrolidone or acrylonitrile are generally known as substances, as are the modified copolymers which can be obtained therefrom by the action of acids or bases and in which the carbonamide groups as a whole or can be partially eliminated from the copolymerized N-vinylcarboxamides and in which the copolymerized comonomers are optionally hydrolyzed. Such partially or fully hydrolyzed copolymers of N-vinylformamide are used, for example, as dry and wet strength agents in the production of paper, as fixatives and as promoters for diketene sizing.

The known polymeric retanning agents for leather are in need of improvement in terms of the fullness, fine and firm grain that they impart to the leather, and also in terms of their dyeing behavior. It is therefore an object of the present invention to provide such retanning agents with improved properties.

Accordingly, the use of N-vinyl units-containing polymers, which by radical-initiated polymerization of a monomer or a monomer mixture

(A) 5 to 100% by weight of an N-vinylamide of the general formula I

H ₂ C = CH NC = 0 (i)

R ¹ R ² and / or an N-vinylamine of the general formula II H ₂ C = CH NH R ² (II)

in which R ¹ and R ² independently of one another denote hydrogen or Cr to C ₆ alkyl,

(B) 0 to 95% by weight of monoethylenically unsaturated carboxylic acids with 3 to 8 carbon atoms, their alkali metal, alkaline earth metal or ammonium salts, anhydrides, esters, amides and / or nitriles,

(C) 0 to 95% by weight of other N-vinyl and / or C-vinyl compounds from the group N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylimidazole, N-vinyl-2-methylimidazole, N-vinyl 4-methyl 3 imidazole, N, N-diallylammonium chloride, vinyl acetate, vinyl propionate, styrene and methylstyrene and

(D) 0 to less than 10% by weight of other copolymerizable monomers,

the sum of the monomers (A) to (D) being 100% by weight and the N-acyl groups derived from the N-vinylamides I being able to be partially or completely removed from the polymers obtained by hydrolytic elimination with acids or bases are,

found in the form of aqueous solutions or dispersions as tanning agents for single tanning, pre-tanning and co-tanning of bare and pelt bones and for retanning leather and fur.

The following vinylcarboxamides are, for example, suitable as monomers (A) of the formula I: N-vinylformamide, N-vinyl-N-methylformamide, N-vinyl acetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethyl acetamide, N -Vinyl propionamide, N-vinyl-N-methyl propionamide and N-vinyl butyramide. From this group of monomers, N-vinylformamide is preferably used.

Suitable monomers (A) of the formula II are, for example, the vinylamines corresponding to the abovementioned vinylcarboxamides (H instead of R ¹ ) with the same radical R ² .

Suitable monomers (B) are monoethylenically unsaturated carboxylic acids having 3 to 8 carbon atoms, in particular having 3 to 6 carbon atoms, such as acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, maleic acid, citraconic acid, methylene malonic acid, allylacetic acid, vinyl acetic acid, crotonic acid, fumaric acid, Mesaconic acid and itaconic acid. The monoethylenically unsaturated carboxylic acids can be used in the copolymerization in the form of the free acid and - if present - the anhydrides or in partially or in completely neutralized form. To neutralize these monomers it is preferred to use alkali metal or alkaline earth metal bases, ammonia or amines, e.g. Sodium hydroxide solution, potassium hydroxide solution, soda, potash, sodium hydrogen carbonate, magnesium oxide, calcium hydroxide, calcium oxide, gaseous or aqueous ammonia, triethylamine, ethanolamine, diethanolamine, triethanolamine, morpholine, diethylene triamine or tetraethylene pentamine.

Further suitable monomers (B) are, for example, the esters, amides and nitriles of the above-mentioned carboxylic acids, for example methyl acrylate, ethyl acrylate, methyl methacrylate, methyl methacrylate, hydroxyethyl acrylate, 4

Hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyisobutyl acrylate, hydroxyisobutyl methacrylate, maleic acid monomethyl ester, maleic acid dimethyl ester, maleic acid monoethyl ester, maleic acid di - ethyl ester, 2-ethyl methacrylate, acrylate ethyl acrylate, amyl ethyl acrylate, acrylate, acrylate -Butyl acrylamide, acrylonitrile, methacrylonitrile, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate and the salts of the last-mentioned monomers with carboxylic acids or mineral acids and the quaternized products.

In a preferred embodiment, the monomers (B) used are acrylic acid, methacrylic acid, maleic acid, maleic anhydride or mixtures thereof.

In the case of the monomers (C), styrene and methylstyrenes, i.e. α-methylstyrene, β-methylstyrene, o-methylstyrene, m-methylstyrene and p-methylstyrene, preferred.

Other copolymerizable monomers (D) include, for example, acrylamidoglycolic acid, vinylsulfonic acid, allylsulfonic acid, methalllylsulfonic acid, styrenesulfonic acid, acrylic acid (3-sulfopropyDester, methacrylic acid (3-sulfopropyl) ester and acrylamidomethylpropanesulfonic acid, and monomers containing phosphonic acid groups, such as vinylphosphonic acid, allylphosphonic acid, allylphosphonic acid and acrylic amidomethane propanephosphonic acid.

It is of course also possible for all four types of monomers (A) to (D) to use mixtures of the monomers mentioned.

Furthermore, graft copolymers of the above-described homo- or copolymers containing N-vinyl units are also used as the graft base with, for example, styrene and / or methylstyrene, acrylonitrile, n-butyl acrylate, n-butyl methacrylate or others already mentioned in the above part To subsume monomers under the claimed polymers. It is of course also possible to use mixtures of all the monomers already mentioned for the grafting of the polymers containing N-vinyl units.

The monomers (A) are preferably used in an amount of 5 to 95% by weight, in particular 10 to 70% by weight, especially 20 to 60% by weight. 5

The monomers (B) are preferably used in an amount of 5 to 95% by weight, in particular 10 to 90% by weight, especially 25 to 75% by weight.

5 The monomers (C) are preferably used in an amount of 0 to 50% by weight, in particular 1 to 50% by weight.

The monomers (D) are preferably used in an amount of 0 to

9% by weight, in particular from 0 to 5% by weight, especially from 0.1 to 10 5% by weight, are used.

In a preferred embodiment, a monomer mixture is exposed

15 10 to 70% by weight of the monomers (A),

10 to 90% by weight of the monomers (B),

0 to 50% by weight of the monomers (C) and 0 to 5% by weight of the monomers (D)

20 a.

The polymers described are prepared by known processes, e.g. solution, precipitation, suspension or emulsion polymerization, using radical-forming compounds.

The polymerization temperatures are usually in the range from 30 to 200 ° C., preferably 40 to 110 ° C. The polymerization takes place in the presence of polymerization inhibitors

30 form radicals under the given polymerization conditions. Suitable initiators (starters) are, for example, hydrogen peroxide, peroxides, hydroperoxides, redox catalysts and in particular non-oxidizing initiators, such as azo compounds which break down into free radicals, such as 2,2'-azobis (2-amidinopropane) dihydro-

35 chloride, 2, 2 '-azo-bis (N, N-dimethyleneisobutyramidine) dihydrochloride, 2, 2' -azo-bis (2, 4-dimethylvaleronitrile), 2, 2 '-azo bis [2-methyl -N- (2-hydroxyethyl) propionamide] or 2,2'-azobisisobutyronitrile. It is of course also possible to use mixtures of different initiators. The amount of starter for

The radical polymerization that is used is in the range of 0.001 to 5 wt .-%, based on the total amount of monomers.

If polymers with low molecular weights are desired, it is possible, for example, to increase the amounts of initiators which are usually used in the polymerization, so that outside the range indicated above for the amounts of initiators. 6 ches lies. Low molecular weight copolymers can also be obtained by working in the presence of polymerization regulators or by using polymerization regulators and higher amounts of initiators than is usually required. Suitable polymerization regulators can be added in amounts of 0.05 to 20 wt.

The polymers described have K values of at least 7, preferably they are 10 to 250, in particular 20 to 100. However, the polymers can also have K values of up to 300. The K values are determined according to H. Fikentscher, Cellulose-Chemie, Volume 13, pages 58 to 64 and 71 to 74 (1932), in aqueous solution at 25 ° C. at concentrations which depend on the K value range are between 0.1% and 5% by weight.

Are obtained from the polymers described by partial or complete elimination of the formyl or Cι ~ to _C6 alkyl-C = 0 inylamiden groups from the copolymerized in the polymer N _V I with formation of amino or ammonium groups hydrolyzed homo- or copolymers which have units of the formula Ia and / or Ha:

CH ₂ \ ^ ^ CH ₂ \

HC HC

• N. R ^l N

R ² R ² H

O

(la) (ha)

In the formulas Ia and Ha, the substituents R ¹ and R ² each have the abovementioned meaning ^¬ weils. Depending on the reaction conditions chosen for the hydrolysis, one contains either partial (for example with degrees of hydrolysis of 3 to 98%, in particular 30 to 90%) or complete hydrolysis of the units la. When copolymers of N-vinylamides I are used, so also the comonomers used can be chemically altered depending on the selected hydrolysis condition, for example, arise from _V inylacetat units of vinyl alcohol units, from Acrylsäureme- methyl ester units of acrylic acid units and from acrylonitrile input units of acrylamide or acrylic acid. 7

The units of the formula Ha can thus be formed either by using N-vinylamines II as monomers (A) or by the described hydrolysis of the units of the formula Ia originating from the N-vinylamide monomers I.

Mineral acids are suitable as hydrolysis agents, e.g. Hydrogen halides, which can be used in gaseous form or in aqueous solution. Hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid and organic acids, e.g. Ci to Cs carboxylic acids and aliphatic or aromatic sulfonic acids. 0.05 to 2, preferably 1 to 1.5 molar equivalents of an acid are required per acyl group equivalent which is to be split off from the copolymerized units Ia.

The hydrolysis of the polymerized units of structure la can also be carried out with the aid of bases, e.g. of metal hydroxides, especially alkali metal or alkaline earth metal hydroxides. Sodium hydroxide or potassium hydroxide is preferably used. The hydrolysis can also be carried out in the presence of ammonia or amines.

The polymer solutions or dispersions obtainable in this way can be used in an outstanding manner as tanning agents in leather and fur production.

The present invention thus also relates to a process for single-tanning, pre-tanning and co-tanning of skin and skin and for retanning leather and skin, which is characterized in that the polymers containing N-vinyl units described are used as tanning agents in the form of aqueous solutions or dispersions starts.

The polymers used according to the invention can be used for tanning pelts and pelts together with the tanning agents of the main tanning, which can be, for example, chrome, aluminum, titanium or zirconium tanning. In this case, the working conditions regarding pH, temperature and duration of the treatment are adjusted to the requirements of the main components of the tanning, the same applies to the treatment apparatus and the liquor length as well as to the aftertreatment. The required amount of the copolymer used according to the invention is normally 0.1 to 20% by weight, in particular 0.5 to 15% by weight, based on the pelt weight.

In particular, the polymers used according to the invention can be used for retanning leather and fur that have already been tanned, for example chrome leather (so-called wet blue), wet white (with, for example, aldehydes 8 or synthetic tanning agents, pre-tanned pelts or pelts) or vegetable tanned leather or fur, can be used in an aqueous liquor. Chrome leather is preferably retanned. This is usually done in such a way that the pickled pelts and skins, for example beef pelts with a gap thickness of 1.5 to 4 mm, with, for example, a chromium-containing tannin such as a chromium III salt, for example Cr (III) sulfate, in tanned in a known manner, the pretanned skins obtained in this way are deacidified and at a pH of 2 to 7, in particular 3.5 to 6, and at temperatures of 15 to 60 ° C., in particular at 25 to 45 ° C., for a time frame from 0.25 to 12 hours are treated with an aqueous solution of the polymers used according to the invention. This treatment takes place, for example, by drumming in a barrel. The required amount of polymers used according to the invention, calculated as 100% active substance, is normally 0.2 to 10% by weight, in particular 0.5 to 5% by weight, based on the shaved weight of the leather. The fleet length is usually 30 to 200% for bare and 100 to 2,000% for bare, each based on the fold weight of the leather.

After and if necessary also before the treatment, the leather or fur is usually adjusted to a pH of 3 to 5, for which purpose, for example, an organic acid such as formic acid or its salts, salts of carbonic acid, or synthetic tanning agents with a neutralizing effect are used , and colors and greases towards the end or after treatment if desired.

The leather or fur retanned in this way can also have been treated with other tanning agents, such as other polymer tanning agents, synthetic or vegetable tanning agents, before retanning with the polymers used according to the invention. The polymers used according to the invention can also be used simultaneously with such additional tanning agents.

All customary agents with a tanning effect on the bare and bare skins can be considered as additional or simultaneously used tanning agents. A comprehensive treatment of such tanning agents can be found, for example, in Ullmann's Encyclopedia of Technical Chemistry, 3rd edition, 11th volume, pages 585 to 612 (1960). Tannin classes to be mentioned individually are the mineral tannins, for example chromium, aluminum, titanium and zirconium salts, the synthetic tannins, the vegetable tannins and the polymer tannins. 9

Single tanning and pre-tanning with the polymers used according to the invention is also possible, but of less interest.

The leathers produced with the polymers used according to the invention give excellent results in terms of light fastness and heat stability. This is particularly noticeable on chrome-pretanned leather. In addition, the polymers used according to the invention have a very good fullness, good fine and firm grain even with small amounts used.

Surprisingly, the disadvantage of polymers based on acrylic and methacrylic acid in the coloring behavior no longer exists in the polymers used according to the invention. Products of this type result in leather with a very dark color, while at the same time achieving very uniform and level colors.

A particular advantage of the polymers used according to the invention can be seen in the fact that, in contrast to conventional syntans, they cannot contain unsulfonated phenols which are harmful to health as residual monomers.

The following examples are intended to illustrate the present invention further, but are not to be understood as a limitation. Unless stated otherwise, percentages always relate to the weight.

Examples

1. Preparation of the polymers

example 1

880 g of water, 98 g of maleic anhydride, 80 g of sodium hydroxide and 2.3 g of sodium dihydrogen phosphate were placed in a 21 glass reactor with anchor stirrer, two automatic feed metering devices and oil bath heating. The pH of the solution was 6.5. The mixture was then heated to 80 ° C. in a gentle stream of nitrogen and a vacuum was applied until the mixture boiled gently (pressure approx. 470 mbar). A mixture of 71 g of N-vinylformamide and 2.5 g of mercaptoethanol (feed 1) and 7.5 g of 2,2′-azobis (2-amidinopropane) dihydrochloride were dissolved in the course of 4 hours in 100 g of water (feed 2), metered in evenly. After the end of the feed, the mixture was polymerized for a further hour. The condensate (a total of 375 g) was distilled off during the entire reaction time. The The resulting solution had a solids content of 34.0%. The K value of the polymer, measured 1% in water, was 48.7.

The polymer solution was then heated to 80 ° C. in the same glass reactor and 80 g of a 50% sodium hydroxide solution were added dropwise within one hour. The mixture was then stirred at this temperature for 2 hours, cooled and adjusted to pH 7.0 with concentrated hydrochloric acid. The degree of hydrolysis of the polymer was 100%.

Example 2

539.5 g of water, 0.66 g of 85% strength phosphoric acid and 0.51 g of 50% strength sodium hydroxide solution were placed in a 21 glass reactor with anchor stirrer, three automatic feed metering devices, reflux condenser and oil bath heating. The pH of the solution was 6.5. Now the mixture was heated to 85 ° C. in a weak stream of nitrogen. After the desired temperature had been reached, a solution of 79.2 g of acrylic acid, 88.0 g of 50% sodium hydroxide solution and 100 G of water (feed 1) and 51.8 g of N-vinylformamide (feed 2) became uniform within two hours added. Half of a solution of 3.25 g of 2,2'-azobis (2-amidino-propane) dihydrochloride in 100 g of H0 (feed 3) was also added in two hours and the rest of feed 3 in a further hour . After the end of the feed, the aqueous solution copolymer was polymerized out at a constant 85 ° C. for two hours. The solution had a solids content of 17%. The K value of the polymer, measured 1% in 5% NaCl solution, was 46.8.

Example 3

454 g of the aqueous copolymer solution from Example 2 were heated to 80.degree. C. in a 11 glass flask equipped with anchor stirrer, reflux condenser and dropping funnel. 27.6 g of 50% sodium hydroxide solution were metered in over the course of 10 minutes and the batch was stirred at 80 ° C. for three hours. The mixture was then cooled and adjusted to pH 7 with 36.6 g of concentrated hydrochloric acid. The degree of hydrolysis of the polymer was 79%. The active substance content of the solution was 12.4%. 11 Example 4

600 g of toluene were placed in a glass reactor with anchor stirrer, four automatic feed metering devices, reflux condenser and oil bath heating and heated to reflux temperature (110 ° C.) under inert gas. 24 g of styrene (feed 1) were then metered in uniformly within one hour. 71 g of N-vinylformamide (feed 2) and 49 g of maleic anhydride, dissolved in 100 g of toluene (feed 3), were run in uniformly over a period of 4 hours. 4.5 g of 1, 1 'azobis (cyclohexane-1-carbonitrile), dissolved in 45 g of toluene, were fed in over the course of 5 hours. After a post-polymerization time of 2 hours, the polymer obtained was filtered off, washed with acetone and dried. The yield of polymer was 144 g. The K value, measured 1% in water, was 35.5.

130 g of the terpolymer obtained were further dissolved in 520 g of water and hydrolyzed with 152 g of 50% sodium hydroxide solution at 80 ° C. for 6 hours. The pH was then adjusted to 7 using concentrated hydrochloric acid. The degree of hydrolysis of the polymer was 80%.

2. Application examples

Example A: Retanning from chrome leather to shoe upper leather

A 1.5 mm thick beef wet blue was rinsed in the usual manner, washed and then deacidified with sodium formate and sodium bicarbonate at 30 ° C. to a pH of 4.5. After washing, 1% of the hydrolyzed copolymer from Example 1, based on the solids content, was drummed for 30 minutes at 35 ° C. in 100% liquor, and then 4% of a commercially available synthetic tanning agent based on a phenolsulfonic acid-formaldehyde condensate were added and again Walked for 90 minutes. The leather was then washed again and dyed in 100% liquor at 50 ° C. with 1% of a commercially available dye within 20 minutes. This was followed by greasing in the same fleet with 5% of a commercially available fat liquor. The mixture was then acidified to pH 3.5 with formic acid. After a short rinse, the leather was stretched out, dried, conditioned and stolled. A leather with very good fullness was obtained with an elastic grip and firm scars. The dyeing with anionic dyes was much more intense, brilliant and level than 12 for comparable commercial products based on acrylic acid, methacrylic acid or maleic acid.

Analogously to Example A, the unhydrolyzed or partially hydrolyzed copolymers from Examples 2 to 4 were used, the properties varying in depth, color depth and fine grain depending on the composition of the products. In any case, the leathers were pitted, especially in the flames and flanks. The colorations were superior to the commercially available polymers in terms of color depth and levelness.

Example B: Retanning of chrome leather in combination with veinable tanning agents to create shoe upper leather

Analogous to example A, a beef wetting blue of fold thickness was used

Washed 1.5 mm and deacidified. The leather was then treated in 100% liquor with 1%, based on the active substance content, of the hydrolyzed copolymer from Example 1 at 40 ° C. within 30 minutes. Then 5% of a commercially available vegetable tanning agent (Mimosa) and 2% of a commercially available resin tanning agent were added to the same liquor and drummed for 90 minutes. The liquor was adjusted to pH 4.2 with formic acid and drummed again for 20 minutes. Analogously to Example A, the mixture was then washed, colored, greased and acidified. A sturdy leather was obtained with excellent fullness and strength, particularly suitable for the firmer shoe type. Despite the use of the vegetable tanning agent, the coloring was very brilliant, regardless and deep in color.

Analogously to Example B, the copolymers from Examples 2 to 4 were used, the properties in terms of fullness, depth of color and levelness also being superior to the commercially available polymers. Example B shows the outstandingly good combinability of the polymers according to the invention with the synthetic or vegetable tanning agents usually used in leather production.

Claims

13 Patent claims

1. Use of polymers containing N-vinyl units, which are produced by radical-initiated polymerization of a monomer or a monomer mixture

(A) 5 to 100% by weight of an N-vinylamide of the general formula I

H ₂ C = CH NC = 0 (I)

R ¹ R ² and / or an N-vinylamine of the general formula II

H ₂ C = CH NH R ² (II)

in which R ¹ and R ² independently of one another are hydrogen or C ₁ -C ₆ -alkyl,

(B) 0 to 95% by weight of monoethylenically unsaturated carboxylic acids having 3 to 8 carbon atoms, their alkali metal, alkaline earth metal or ammonium salts, anhydrides, esters, amides and / or nitriles,

(C) 0 to 95% by weight of other N-vinyl and / or C-vinyl compounds from the group N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylimidazole, N-vinyl-2-methylimidazole, N- Vinyl-4-methylimidazole, N, N-diallylammonium chloride, vinyl acetate, vinyl propionate, styrene and methylstyrene and

(D) 0 to less than 10% by weight of other copolymerizable monomers,

where the sum of the monomers (A) to (D) is 100% by weight and the N-acyl groups derived from the N-vinylamides I are partially or completely removed from the polymers obtained by hydrolytic cleavage with acids or bases are available,

in the form of aqueous solutions or dispersions as tanning agents for single tanning, pre-tanning and co-tanning of bare and pelt and for retanning leather and fur. 14

2. Use of N-vinyl unit-containing polymers according to claim 1, which by radical-initiated polymerization of a monomer mixture

10 to 70% by weight of the monomers (A), 10 to 90% by weight of the monomers (B), 0 to 50% by weight of the monomers (C) and 0 to 5% by weight of the monomers (D )

are available.

3. Use of N-vinyl unit-containing polymers according to claim 1 or 2, which are obtainable by radical-initiated polymerization using acrylic acid, methacrylic acid, maleic acid, maleic anhydride or mixtures thereof as monomers (B).

4. Use of polymers containing N-vinyl units as claimed in claims 1 to 3, the polymers having K values according to Fikentscher from 7 to 250.

5. A process for single tanning, pre-tanning and co-tanning of skin and skin and for retanning leather and skin, characterized in that polymers containing N-vinyl units according to claims 1 to 4 are used as tanning agents in the form of aqueous solutions or dispersions.